In the related art, an example of such a pulse period calculation device is a heartbeat measurement device disclosed in Patent Document 1.
In this heartbeat measurement device, a peak holding signal having a stepped waveform is generated as a result of a heartbeat waveform signal being subjected to peak holding by a peak holding unit. A pattern detection and period determining unit detects a pattern in which there are successive increases in signal level from the generated peak holding signal and matches this pattern to a P wave and an R wave in an electrocardiogram. Then, when the time interval between a peak that corresponds to the P wave and a peak that corresponds to the R wave is within a predetermined range and the difference in level value between the peaks exceeds a threshold, these peaks are regarded with certainty as being peaks that correspond to the P wave and the R wave and the larger peak is specified as being the R wave. When a pattern in which there are successive increases in signal level is not detected, a pattern of successive decreases in signal level is complimentarily detected and this pattern is matched to an R wave and a T wave in an electrocardiogram. Then, regarding the peak corresponding to the R wave and the peak corresponding to the T wave, the larger of these peaks is specified as the R wave by performing similar processing to as in the case of the P wave and the R wave. The heart rate is then calculated from the time interval between R waves specified in this way.
In addition, in the related art, there is also a heartbeat measurement system disclosed in Patent Document 2, as an example of such a pulse period calculation device.
In this heartbeat measurement system, a heartbeat signal is detected from a measurement target by a signal detection device. The detected heartbeat signal is subjected to time division by a signal processing device and the obtained successive signals are compared to each other by the signal processing device. A peak value of the heartbeat signal is detected from the result of this comparison. In addition, the signal processing device generates a peak value group containing one or a plurality of peak values in heartbeat units of the heartbeat signal and standardizes each peak value of the peak value group by dividing each peak value of the peak value group by the largest peak value of the peak value group. Accordingly, by subjecting the standardized signal to addition and multiplication, the fine structure of the signal, which was liable to be overlooked conventionally, is revealed.
In addition, in the related art, there is also a pulse wave analysis device disclosed in Patent Document 3, as an example of such a pulse period calculation device.
In this pulse wave analysis device, a pulse wave is obtained on the basis of a pulse wave signal from a pulse wave sensor and the top point (peak) of the pulse wave corresponding to the contraction period of the heart is obtained as a result of a data processing device including the pulse wave analysis device searching for the top point of the obtained pulse wave. It is determined whether time intervals adjacent to the obtained top point are less than a predetermined time period expressed by a top point search correction coefficient t3. In this determination, if it is determined that the time intervals adjacent to the top point are equal to or more than the predetermined time period, the detected top point is counted as a true top point, which is not noise or the like, and the average number of times this top point occurs in one minute is calculated as the pulse rate. In addition, by extracting, or subtracting the base line of the pulse wave, a modified pulse wave that is close to a sin wave is obtained. When this modified pulse wave is subjected to complex demodulation analysis at the frequency of the pulse wave, the instantaneous frequency expressing a frequency f between peaks of the pulse waves is obtained and the pulse interval, which is the period T, is obtained from the frequency f. The top point search correction coefficient t3 is updated from the average value of the pulse interval and top point searching is accurately performed by removing noise.